docs(FR-2650): recapture dashboard.png in ko/ja/th

First entry of the incremental MCP-based recapture under FR-2650.
Progress tracked at packages/backend.ai-webui-docs/.agent-output/fr-2650-progress.md (gitignored).

Next sessions should: read the progress file, pick next pending entries,
capture via Playwright MCP with proper per-image context (admin vs user mode,
specific tabs, modals vs pages), update progress, commit batch, push.

Author: ironAiken2